The present invention relates to a control device for vulcanization chambers in vulcanization presses, said device being of the type comprising: a fluid-operated actuator housed in a vulcanization press bed; a drive rod coaxially emerging from the fluid-operated actuator and movable, upon operation of a lower piston operatively housed in the actuator, from a minimally drawn-out position to a maximally drawn-out position relative to the actuator itself. The device includes a movable sealing disc, coaxially fastened to the drive rod; a fixed sealing disc, coaxially fixed relative to the fluid-operated actuator; a flexible substantially sleeve-shaped vulcanization chamber on an upper end edge and a lower end edge which is sealingly fastened to said movable disc and fixed disc respectively; first stop means to fix the positioning of the drive rod to the maximally drawn-out position; and second stop means to fix the positioning of the drive rod to the minimally drawn-out position.
This device puts into practice a control process for vulcanization chambers in vulcanization presses of the type involving the use of a substantially sleeve-shaped vulcanization chamber having an upper end edge engaged to a sealing disc axially movable upon command of a fluid-operated actuator fastened to a vulcanization press bed, and a lower end edge engaged to a sealing disc which is fixed relative to said fluid-operated actuator. The disclosed process includes the steps of: moving the movable disc apart from the fixed disc upon a thrust action exerted by said fluid-operated actuator, so as to extend the vulcanization chamber according to a substantially cylindrical conformation; moving the movable disc close to the fixed disc and simultaneously introducing working fluid into the vulcanization chamber, in order to cause the chamber to radially expand within a mold associated with said press.
It is known that in vulcanization presses of the so-called "B.O.M." (Bag-O-Matic) type, used in tire vulcanization, the use of a vulcanization chamber made of elastomeric material is provided, which is substantially in the form of a sleeve and which lends itself to being brought from an extended condition, in which it vertically projects in a cylindrical conformation from the lower portion of the mold, to enable the removal of the vulcanized tire and the introduction into the same mold of a new tire to be vulcanized, to a radially-expanded condition in which the chamber, inflated under pressure, acts against the inner walls of the tire being made in order to ensure the adhering thereof against the inner sides of the mold encircling it.
In particular, the vulcanization chamber has an upper end edge sealingly fastened to a movable disc, rigidly connected to a drive rod. This drive rod is operable by a lower piston being part of a fluid-operated actuator fixedly housed in the press bed.
The vulcanization chamber also has a lower end edge which is sealingly engaged to a fixed disc coaxially screwed to the upper end of the actuator, from which the drive rod emerges. This fixed disc is disposed substantially flush with the lower portion of the mold.
By introducing working fluid, generally water or steam under pressure, into the fluid-operated actuator, the drive rod is axially moved by the lower piston, between a maximally drawn-out position to a minimally drawn-out position relative to the actuator itself. Corresponding to these positions is the extended and radially-expanded conditions respectively of the vulcanization chamber.
Also housed in the fluid-operated actuator is an upper piston, the essential function of which is to define the stop positions of the drive rod, and therefore the movable disc, at said maximally and minimally drawn-out locations.
To this end, the upper piston carries one cylindrical spacer designed to act in abutment against the upper end of the actuator in order to give the piston itself a predetermined positioning, capable of suitably restraining the upstroke of the lower piston. Usually the upstroke is limited to such an extent that in the maximally drawn-out position of the rod, the chamber is extended and in tension so as to enable the vulcanized tire to be discharged and a new raw carcass ready for vulcanization to be charged.
The spacer performs the function of limiting the chamber elongation and the consequent pulling effort applied thereto within safety values; it will be apparent that in the absence of this spacer the vulcanization chamber, under the thrust exerted by the upper piston (due to the high feed pressure of the working fluid in the actuator, generally not lower than 1.8 MPa) would undergo elongations and would be subjected to too high efforts that would impair the life of the chamber.
Also associated with the upper piston is a second spacer of cylindrical tubular configuration, disposed coaxially with the first spacer and internally thereof. The second spacer is slidably passed through by the drive rod and emerges from the fluid-operated actuator, at the upper part thereof, in order to stop the downward motion of the movable disc and thereby define the axial positioning of the same in the minimally drawn-out position of the rod.
In current presses of the B.O.M. type there is also provision for the positioning of the movable disc to be fixed at different locations (within a limited range) along the end portion of the drive rod, depending upon the spacer size and the extension of the associated chamber, in order to achieve the expected chamber elongation and/or for other reasons.
The foregoing being stated, it is noted that presently presses of the B.O.M. type involve long idle times when it is necessary to carry out the replacement of the vulcanization chamber. It is in fact necessary to wait for the press cooling taking place before an operator may then be able to disassemble the fixed and movable discs in order to remove the existing chamber, dismantle the actuator so as to replace the spacers by other spacers suitable for the new chamber to be installed and then reassemble the actuator and discs to the new chamber.
In addition, it is also necessary to wait for the press again to reach the working temperature before the vulcanization cycle of the tires can be restarted.
The Applicant has already developed and put into practice a quick coupling device enabling the immediate removal of the discs together with the chamber in order to carry out the quick replacement of said chamber, also in an automatic manner, without waiting times being necessary for the press cooling and subsequent heating.
In this device (see U.S. Pat. No. 4,872,822) provision is substantially made for a grasping head to be mounted to the upper end of the drive rod, inside which head a plurality of circumferentially distributed pins is housed, said pins being operable from the outside of the head so as to be brought from an engaging position in which they radially project from respective openings exhibited by the head to a disengaging condition in which they are radially retracted within the head. In the engaging position the pins lend themselves to hold the disc associated with the rod by entering a circumferential groove formed on an internal cylindrical surface of the disc, whereas in the disengaged position the disc is clear of the pins and can therefore be removed from the head.
In accordance with the above device the lower disc is also provided to be detachably fastened to a grasping ring provided with a plurality of circumferentially distributed latches that are radially movable, upon angular rotation of a drive nut provided with circumferential cams, between an engaged position in which they radially project towards the inside of the ring to a disengaged position in which they are radially retracted in spaced apart relation with respect to the ring axis. In the engaged position the latches penetrate into a circumferential groove formed on an outer cylindrical surface of the disc in order to firmly hold said disc, whereas in the disengaged position disc removal is allowed.
However the above described device lends itself to be used only on presses of recent vintage, in which both discs are axially movable independently of each other and in which the replacement of the vulcanization chamber does not involve a long additional time for the replacement of spacers or the like within the actuator controlling the disc shifting.
In accordance with the present invention it has been found that in order to enable the use of a quick coupling device on a press of the B.O.M. type the positioning of the movable disc must be suitably fixed in the vicinity of the upper end of the drive rod, and the stopping of the rod upstroke to the maximally drawn-out position must be determined by the tensile strength opposed by the chamber in an extended condition, to the thrust exerted by the actuator.